initial day 13

src/AOC/Challenge/Day13.hs

@@ -22,8 +22,8 @@
 --     will recommend what should go in place of the underscores.
 
 module AOC.Challenge.Day13 (
-    -- day13a
-  -- , day13b
+    day13a
+  , day13b
   ) where
 
 import           AOC.Prelude
@@ -45,16 +45,79 @@ import qualified Text.Megaparsec                as P
 import qualified Text.Megaparsec.Char           as P
 import qualified Text.Megaparsec.Char.Lexer     as PP
 
+-- negate (i-x-0.5) + x+0.5
+-- -i+x+0.5+x+0.5
+-- -i+x+x+1
+
+findRefl :: Set Point -> IntSet
+findRefl pts = IS.fromList findHoriz
+            <> IS.fromList ((*100) <$> findVert)
+  where
+    Just (V2 (V2 xMin yMin) (V2 xMax yMax)) = boundingBox' pts
+    cols :: IntMap IntSet
+    cols = IM.fromListWith (<>)
+      [ (x, IS.singleton y)
+      | V2 x y <- toList pts
+      ]
+    rows :: IntMap IntSet
+    rows = IM.fromListWith (<>)
+      [ (y, IS.singleton x)
+      | V2 x y <- toList pts
+      ]
+    findHoriz = flip filter [xMin+1 .. xMax] $ \x ->
+      let (lt, gt) = IM.spanAntitone (< x) cols
+       in and $ zipWith (==) (snd <$> IM.toDescList lt) (snd <$> IM.toAscList gt)
+      -- let cols = IntMap IntSet
+      --     cols = IM.fromListWith (<>) $ toList pts
+      -- let (lt,gt) = S.partition ((< x) . view _x) pts
+      --     gt' = S.map (over _x ((+ (x-1)) . negate . subtract x)) gt
+      --     inters = lt `S.intersection` gt'
+      --  in inters == lt || inters == gt'
+    findVert = flip filter [yMin+1 .. yMax] $ \y ->
+      let (lt, gt) = IM.spanAntitone (< y) rows
+       in and $ zipWith (==) (snd <$> IM.toDescList lt) (snd <$> IM.toAscList gt)
+    -- findVert = flip find [yMin+1 .. yMax] $ \y ->
+    --   let (lt,gt) = S.partition ((< y) . view _y) pts
+    --       gt' = S.map (over _y ((+ (y-1)) . negate . subtract y)) gt
+    --       inters = lt `S.intersection` gt'
+    --    in inters == lt || inters == gt'
+      -- let flipped = S.map (\(V2 i j) -> V2 (-i + 2*x+1) j) pts
+      --     -- symDiff = (flipped S.// pts) <> (pts S.// flipped)
+      --     -- inters = S.intersection flipped pts
+      --  in shiftToZero' (flipped `S.difference` pts) == shiftToZero' (pts `S.difference` flipped)
+      -- x <$ guard (S.map (\(V2 i j) -> V2 (negate (i - x)) j) pts == S.map (\(V2 i j) -> V2 (i - x) j) pts)
+    -- findVert = flip find [yMin .. yMax] $ \y ->
+    --   let flipped = S.map (\(V2 i j) -> V2 i (-j + 2*y+1)) pts
+    --       -- symDiff = (flipped S.// pts) <> (pts S.// flipped)
+    --       -- inters = S.intersection flipped pts
+    --    in shiftToZero' (flipped `S.difference` pts) == shiftToZero' (pts `S.difference` flipped)
+    --   -- y <$ guard (S.map (\(V2 i j) -> V2 i (-j + 2*y)) pts == S.map (\(V2 i j) -> V2 i (j - y)) pts)
+
+-- condenseRefl :: Maybe Int -> Maybe Int -> Maybe Int
+-- condenseRefl horiz vert = horiz <|> ((* 100) <$> vert)
+
 day13a :: _ :~> _
 day13a = MkSol
-    { sParse = Just . lines
+    { sParse = noFail $ map (parseAsciiSet (== '#')) . splitOn "\n\n"
     , sShow  = show
-    , sSolve = Just
+    -- , sSolve = noFail $ map findRefl
+    , sSolve = fmap sum . traverse (fmap fst . IS.minView . findRefl)
     }
 
+findSmudge :: Set Point -> Maybe Int
+findSmudge pts = flip firstJust (V2 <$> [xMin .. xMax] <*> [yMin .. yMax]) \pt ->
+    let newRefl = findRefl (over (contains pt) not pts)
+        isNew = newRefl `IS.difference` origRefl
+     in fst <$> IS.minView isNew
+     -- in guard (newRefl /= origRefl) *> (fst <$> IS.minView isNew)
+    -- mfilter (/= origRefl) $ findRefl (over (contains pt) not pts)
+  where
+    origRefl = findRefl pts
+    Just (V2 (V2 xMin yMin) (V2 xMax yMax)) = boundingBox' pts
+
 day13b :: _ :~> _
 day13b = MkSol
     { sParse = sParse day13a
     , sShow  = show
-    , sSolve = Just
+    , sSolve = fmap sum . traverse findSmudge
     }

test-data/2023/13a.txt

@@ -0,0 +1,32 @@
+#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.
+
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#
+>>> 405
+#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.
+>>> 5
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#
+>>> 400

test-data/2023/13b.txt

@@ -0,0 +1,32 @@
+#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.
+
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#
+>>> 400
+#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.
+>>> 300
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#
+>>> 100